How can I look up or create a shortcut?
Edge slide is indeed a special case, triggered through double G (grab mode -> edge slide). For this reason it doesn't show a key map entry.

You can however assign it yourself a key in the input configuration of user preferences. Under 3D View open the Mesh operator tree, scroll down and press Add New. In the first box write "transform.edge_slide", and give a key or key combo to trigger this. After that you should see the shortkey in the operator search menu as well. In the example image below I've used the equal sign.